Sunroofs or canopies have been used in automobiles and in other land and marine vehicles to provide the capability to vary the visible light entering such vehicles. Land and marine vehicles as well as aircraft have also utilized interior partitions to separate, for reasons of privacy, passengers from one another or operators of such vehicles from passengers. Various types of smoked or glazed windows are used in land and marine vehicles as well as aircraft to provide privacy to the passengers or operators.
Sunroofs utilized heretofore have comprised a slidably arranged portion of a vehicle's roof that may be open or closed either manually or automatically, as desired by the vehicle operator or passenger. Other sunroof configurations, sometimes called "moonroofs", do not open and close but provide a see-through section in the roof which lets ambient light enter the interior of the vehicle.
Partitions in vehicle interiors are often found in vehicles such as limousines. They are utilized to divide the passenger compartment of such vehicles from the driver's area. They may be utilized to provide privacy for the passengers. Exterior windows providing privacy to the passengers are often found in vehicles such as limousines, vans and recreational vehicles (RVs).
Safety glazing materials, in comparison with ordinary sheet glass, plate glass or float glass, are intended to reduce the likelihood of injury or the severity of injury in the event of their breakage. Such safety glazing materials often are incorporated in land or marine vehicles or aircraft where there is elevated exposure to impact or breakage. Such materials may be used in sunroofs, vehicle partitions and privacy windows. One safety glazing material may be superior for one type of hazard, whereas another may be superior against another type. Since accident conditions are not standardized, no one type of safety glazing material can be shown to possess the maximum degree of safety under all conditions, against all conceivable hazards.
Glass and films with selective light transmission properties have heretofore been used to reduce or eliminate glare, hot spots and/or thermal load on buildings or vehicles. Generally, such materials reduce visible light transmission and preferentially reflect infrared light. In some cases, such materials simply absorb light throughout the visible and/or infrared spectrum. These materials may be built into buildings or vehicles or applied afterward on a retrofit basis. In many cases where glass is used in buildings as well as in vehicles, safety glazing properties, as discussed above, are required.
There are three aspects of discomfort which these materials are designed to reduce. The first is glare, or high brightness in the visible spectrum, generally directly from the sun or sun reflection. The second is hot spots where the sun rays fall on a portion of the vehicle or building and heated far above the ambient air temperature, or where the sun's rays directly heat people. The third is general heat load, caused by sunlight, both direct and reradiated from outside the building or vehicle, which increases air temperature in the building or vehicle.
Most materials which reduce discomfort are passive and therefore have undesirable features. While they reduce glare, hot spots and thermal load, they do so at all times whether such reduction is desired or not. In many cases such as at night, or cloudy days, in morning or evening, there is no need for glare, hot spot or thermal load reduction, yet passive materials continue to reduce visibility at these times. Further, the sun's thermal heating can reduce energy use in winter, but passive materials cut the beneficial effect of the sun's heating in winter.
For these reasons a practical variable light transmission material has been sought. Such a material would reduce glare, hot spots and/or thermal load on bright summer days, but would switch to a high visibility high transmission window at all other times. Such a material would save energy and eliminate the space, weight and maintenance required for drapes.